All-dielectric, self-supporting, loose-tube optical fiber cable

ABSTRACT

A method for producing an optical fiber cable which improves stability by attaching an Aramid yarn near the core in parallel to an axial direction of the optical cable and solves structural problems of the cable by soaking an Aramid yarn into an epoxy resin is disclosed. This optical cable producing method uses a tensile material for improvement of tensile property, and includes the steps of soaking the tensile material into an epoxy resin, and attaching the tensile material to the optical cable in parallel to the axial direction of the optical cable.

TECHNICAL FIELD

The present invention relates to arrangement and fixing method of atension member for an all-dielectric self-supporting (ADSS) opticalcable, and more particularly to an optical cable capable of improvingtensile force of the cable and preventing structural instability causedby bending.

BACKGROUND ART

Recently, demands for optical communication are abruptly increased inconcert with the development of information communication techniques.Accordingly, the demand for the optical cables is also tending toincrease. ADSS (All-Dielectric Self-Supporting Cable) is one of aerialoptical cables. This ADSS cable is designed to include 2 to 144 stripsof optical fibers.

Main features of the ADSS cable are that it is a completely nonmetalliccable, and capable of self-supporting. In addition, high tensilestrength and tracking resistance are possessed therein. Moreover, theADSS cable may be installed using an existing pylon with a lowconstruction cost, so the ADSS cable is expected to show increaseddemand in the future.

The ADSS cable generally includes a core having an optical fiber unitand positioned at the center, and a sheath for protecting the core.Since the ADSS cable should ensure a life for a long time (about 30years), relevant mechanical performance of the cable such as tensileproperty and bending of the cable is essential. In order to improve thetensile property of the ADSS cable, a tensile member is respectivelyadopted between the core and the sheath.

Conventionally, a tensile member in which an Aramid yarn is strandedwith keeping regular pitches is used in the aforementioned sheath.However, this conventional method shows a deteriorated tensile propertyin an axial direction of the cable due to the load dispersion in aradial direction according to the Wire Rope theory, rather than thelinear member. In addition, the cable is extended due to its own weightafter the optical cable is installed, thereby generating a torsion,which is a factor of performance deterioration.

However, despite such problems; the reason of stranding the Aramid yarnin the convention method is that it prevents structural instability ofthe cable caused by inclination of the Aramid yarn, which is apt to begenerated in bending the cable.

As described above, the conventional method for manufacturing an opticalcable arouses deterioration of the tensile property and torsion of thecable, thereby giving optical losses and exerting a bad influence uponthe life of the cable. In order to solve these problems, an improvedmethod is proposed to use SZ-stranding, namely doubly stranding theAramid yarn in opposite directions with keeping the pitch as it is.

However, the SZ-stranding method requires to add a complex process inthe optical cable manufacturing procedure, thereby arousing severalproblems, such as increase of a production cost and a weight of thecable. In addition, since this method cannot be applied to an opticalcable having a small diameter, the Aramid yarn should be stranded in onedirection in such an optical cable.

DISCLOSURE OF INVENTION

The present invention is designed to solve the problems of the priorart, and therefore an object of the invention is to provide an ADSScable capable of showing an excellent tensile property together withpreventing structural instability, which is apt to be generated during abending behavior of the optical cable.

In order to accomplish the above object, the present invention providesan ADSS optical cable including a central tensile member extended in alongitudinal direction; at least one optical fiber for transmitting anoptical signal; at least one tubular buffer receiving the at least oneoptical fiber therein and arranged around the central tensile memberadjacently, the tubular buffer being twisted on the center of thecentral tensile member; an inner sheath extended in the longitudinaldirection with surrounding the at least one tubular buffer; an outertensile member extended in the longitudinal direction with surroundingthe inner sheath; and an outer sheath extended in the longitudinaldirection with surrounding the outer tensile member, wherein the outertensile member includes a plurality of tensile wires extended in thelongitudinal direction in parallel without intentional twisting on thecentral tensile member; and an adhesive resin for connecting the tensilewires adjacent to each other.

In addition, the outer tensile member is preferably configured so thatthe plurality of tensile wires arranged in parallel without intentionaltwisting are soaked in the adhesive resin.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of preferredembodiments of the present invention will be more fully described in thefollowing detailed description, taken accompanying drawings. In thedrawings:

FIG. 1 is a sectional view showing an ADSS cable according to apreferred embodiment of the present invention; and

FIG. 2 shows a structure of an external tensile member according to thepresent invention.

BEST MODES FOR CARRYING OUT THE INVENTION

Hereinafter, preferred embodiments of the present invention will bedescribed in detail with reference to the accompanying drawings.

FIG. 1 is a sectional view showing an ADSS (All-DielectricSelf-Supporting) optical cable according to a preferred embodiment ofthe present invention.

As shown in FIG. 1, the optical cable of the present invention has acentral tensile member 2 extended in a longitudinal direction. Thecentral tensile member 2 has substantial tensile strength andcompressive strength.

Around the central tensile member 2, at least one optical fiberaggregation is stranded or at least one optical fiber aggregation and atleast one filler 5 are stranded together.

The optical fiber aggregation is composed of at least one optical fiber1 and a tubular buffer 4 loosely surrounding the optical fiber 1. Thatis to say, the optical fiber 1 is loosely received in the tubular buffer4.

The optical fiber 1 is preferably SMF (Single Mode Fiber), MMF (MultipleMode Fiber), DSF (Dispersion Shift Fiber) or NZDSF (Non-Zero DispersionShift Fiber), having a core layer and a clad layer.

The tubular buffer 4 is formed by extrusion in the longitudinaldirection with receiving the at least one optical fiber 1. The tubularbuffer 4 preferably adopts a thermoplastic resin, particularly PBT(polybutyleneterephthalate).

A well-known waterproof jelly is filled in the tubular buffer 4, namelyin a gap between the optical fibers 1.

The filler 5 surrounding the central tensile member 2 together with theoptical fiber aggregation is preferably made of polyethylene material.

In addition, the optical cable of the present invention may include aconventional water-blocking tape 6 extended in the entire length of thecable with surrounding the optical fiber aggregation. Thiswater-blocking tape 6 may be made of water-absorbing materials orcontain such materials. A gap between the tubular buffer 4 in an innerspace surrounded by the water-blocking tape 6 is also preferably filledwith a well-known waterproof jelly.

In addition, the optical cable of the present invention includes aninner sheath 7 extended in the longitudinal direction with surroundingthe water-blocking tape 6. This inner sheath 7 is formed by extrudingpolymer materials such as black polyethylene around the water-blockingtape 6.

The optical cable of the present invention may further include an outertensile member 8 extended in the longitudinal direction of the cable.The outer tensile member 8 is configured as shown in FIG. 2.

That is to say, the outer tensile member 8 includes a plurality oftensile wires extended in the longitudinal direction in parallel withoutany intentional twisting, and an adhesive resin for connecting thetensile wires. The tensile wire preferably adopts an Aramid yarn, andthe adhesive resin preferably adopts an epoxy resin having excellentadhesive force together with superior mechanical features.

The outer tensile member 8 is made by arranging Aramid yarns in parallelwithout any intentional twisting, and then soaking the Aramid yarns inthe epoxy resin. If the Aramid yarn is soaked in the epoxy resin asmentioned above, the epoxy resin is completely permeated into poresbetween the Aramid yarns to generate the tensile member configured asshown in FIG. 2.

The Aramid yarn supports tensile force applied to the cable afterinstallation, and the adhesive resin increases combining force betweenbroken Aramid yarns and improves structural instability of the Aramidyarn, which is apt to arise when the cable is bent.

The optical cable of the present invention may further include an outersheath 9 extended in the longitudinal direction with surrounding theouter tensile member 8. The outer sheath 8 is also formed by extrudingpolymer materials such as black polyethylene around the outer tensilemember 8, similarly to the inner sheath 7.

In the conventional method, a loss of the tensile property occurs due toa radial component of force generated in the optical cable. However, inthe present invention, since the tensile member is attached to the cablein a straight way, namely so that the tensile member has an infinitepitch, 100% of the tensile property may be entirely used as an axialtensile force of the cable.

Thus, it is possible to make an optical cable having excellentperformance with a small amount of tensile materials rather than theconventional making method. In addition, since the torsion generated inextending the optical cable may be removed, the present invention mayensure more stable performance of the optical fiber.

Moreover, the epoxy resin of the present invention combines thepartially broken tensile materials, thereby improving the tensilestrength better than the conventional tensile materials. In addition,after the epoxy resin is cured, the excellent mechanical performance ofthe epoxy resin makes the cable keep structural stability when the cableis bent.

Advantages of the present invention will be more apparent from thefollowing comparative embodiments described below.

COMPARATIVE EMBODIMENT 1

Axial strains (or, tensile properties) of the ADSS optical cable made bythe present invention and the optical cable made by the conventionalmethod are comparatively measured, and the results are shown in thefollowing table 1.

The conventional cable used in this comparative evaluation has a pitchof 200 mm, 500 mm, 700 mm, 1000 mm or infinite, and the tensile propertyof the cable is evaluated at first.

Comparing the optical cable of the present invention with theconventional optical cable in view of tensile property, it would beknown that the optical cable of the present invention shows 100% oftensile property. Meanwhile, the conventional optical cable cannotrealize the tensile property of the optical cable up to 100% sincediameter reduction is increased as the pitch is small. In addition, theaxial strain of the optical cable is increased according to such aresult, thereby generating stress on the optical fiber. Resultantly,this stress acts as a factor of causing an optical loss.

COMPARATIVE EMBODIMENT 2

The comparative embodiment 2 performs comparative experiments fortorsion of the ADSS optical cable made by the present invention and theoptical cable made by the conventional method. Its measurement resultsare well shown in the following table 2.

The present invention also shows nearly no torsion like the results ofthe comparative embodiment 1. Thus, the ADSS optical cable of thepresent invention shows more excellent torsion stability than theoptical cable made by the conventional method.

The present invention has been described in detail. However, it shouldbe understood that the detailed description and specific examples, whileindicating preferred embodiments of the invention, are given by way ofillustration only, since various changes and modifications within thespirit and scope of the invention will become apparent to those skilledin the art from this detailed description.

INDUSTRIAL APPLICABILITY

According to the present invention, it is possible to make an opticalcable with excellent mechanical tensile properties together with givinga solution to the structural instability of the optical cable by soakingthe tensile materials into the epoxy resin.

In addition, by using a smaller amount of tensile materials, a cost formaking the optical cable is lowered.

1. An ADSS (All-Dielectric Self-Supporting) optical cable comprising: acentral tensile member extended in a longitudinal direction; at leastone optical fiber for transmitting an optical signal; at least onetubular buffer receiving the at least one optical fiber therein andarranged around the central tensile member adjacently, the tubularbuffer being twisted on the center of the central tensile member; aninner sheath extended in the longitudinal direction with surrounding theat least one tubular buffer; an outer tensile member extended in thelongitudinal direction with surrounding the inner sheath; and an outersheath extended in the longitudinal direction with surrounding the outertensile member, wherein the outer tensile member includes: a pluralityof tensile wires extended in the longitudinal direction in parallelwithout intentional twisting on the central tensile member; and anadhesive resin for connecting the tensile wires adjacent to each other.2. An ADSS optical cable according to claim 1, wherein the outer tensilemember is configured so that the plurality of tensile wires arranged inparallel without intentional twisting are soaked in the adhesive resin.3. An ADSS optical cable according to claim 2, wherein the tensile wireis an Aramid yarn.
 4. An ADSS optical cable according to claim 2,wherein the tensile wire has an infinite pitch.
 5. An ADSS optical cableaccording to claim 2, wherein the adhesive resin is an epoxy resin. 6.An ADSS optical cable according to claim 2, further comprising at leastone polyethylene filler arranged around the central tensile memberadjacently and twisted on the center of the central tensile membertogether with the tubular buffer.
 7. An ADSS optical cable according toclaim 2, further comprising a water-blocking tape arranged in the innersheath with surrounding the tubular buffer to prevent external moisturefrom penetrating into the optical fiber.
 8. An ADSS optical cableaccording to claim 7, further comprising a waterproof jelly filled in agap between the optical fibers in the tubular buffer and in a gapbetween the tubular buffers in the water-blocking tape.
 9. An ADSSoptical cable according to claim 2, wherein the plurality of opticalfibers are loosely received in the tubular buffer.